t9390: avoid using `colrm`

While it is true that `colrm` is available on macOS by default, and even
in Ubuntu (thanks to the `bsdmainutils` package), it is not available on
Windows.

Let's use `cut` instead.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

t/t9390-filter-repo.sh

@@ -1675,7 +1675,7 @@ test_expect_success 'tweaking just a tag' '
 
 test_expect_success '--version' '
 	git filter-repo --version >actual &&
-	git hash-object ../../git-filter-repo | colrm 13 >expect &&
+	git hash-object ../../git-filter-repo | cut -c 1-12 >expect &&
 	test_cmp expect actual
 '